#include<fstream>

using namespace std;

ifstream in("factorial.in");
ofstream out("factorial.out");

int zero(int n)
{
	int r=0;
	while(n)
	{
		r+=n/5;
		n/=5;
	}
	return r;
}
int caut(int x)
{
	int st=1,dr=100000000,mij;
	while(st!=dr)
	{
		mij=(st+dr)/2;
		if(zero(mij)>=x)
			dr=mij;
		else st=mij+1;
	}
	if(zero(st)==x)
		return st;
	return -1;
}

int main()
{
	int p;
	in>>p;
	out<<caut(p)<<"\n";
	in.close();
	out.close();
}